Method of producing lithium ion cathode materials

ABSTRACT

A method of producing Li y [Ni x Co 1−2x Mn x ]O 2  wherein 0.025≦x≦0.5 and 0.9≦y≦1.3. The method includes mixing [Ni x Co 1−2x Mn x ]OH 2  with LiOH or Li 2 CO 3  and one or both of alkali metal fluorides and boron compounds, preferably one or both of LiF and B 2 O 3 . The mixture is heated sufficiently to obtain a composition of Li y [Ni x Co 1−2x Mn x ]O 2  sufficiently dense for use in a lithium-ion battery cathode. Compositions so densified exhibit a minimum reversible volumetric energy characterized by the formula [1833−333x] measured in Wh/L.

CROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This application claims priority from provisional application No.60/454,884 filed on Mar. 14, 2003.

FIELD OF THE INVENTION

[0002] The present invention relates to lithium-ion batteries. Moreparticularly, the present invention relates to a method of densifyingcompositions useful to make electrodes for lithium-ion batteries.

BACKGROUND OF THE INVENTION

[0003] Lithium-ion batteries typically include an anode, an electrolyte,and a cathode that contains lithium in the form of a lithium-transitionmetal oxide. Such lithium-transition metal oxides typically includeLiCoO₂, LiNiO₂ and Li(NiCo)O₂. A lithium-transition metal oxide that hasbeen proposed as a replacement for LiCoO₂ isLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ which adopts the α-NaFeO₂ type structureand can be regarded as the partial substitution of Ni²⁺ and Mn⁴⁺ (1:1)for Co³⁺ in LiCoO₂. Li_(y)[Ni_(x)Co_(1−2x)Mn _(x)]O₂ materials preparedat 900° C. exhibit good cell performance and appear to be much lessreactive with electrolytes at high temperatures compared to LiCoO₂ whencharged at high voltage. However, the material density and thus theresulting electrode density of samples previously reported are lowerthan required for many industrial applications of lithium-ion batteries.

[0004] Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ with x being in the range of 0.25to 0.375 and y being in the range of 0.9 to 1.3 can deliver a stablecapacity of about 160 mAh/g using a specific current of 40 mA/g whencycled between 2.5 V and 4.4 V. Because both nickel and manganese areless expensive than cobalt, Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ appears as apromising composition to replace LiCoO₂. One undesirable feature ofLi_(y)[Ni_(x)CO_(1−2x)Mn_(x)]O2 compounds, however, is their low densityachieved by the known synthesis of starting from a co-precipitation ofhydroxides followed by a heat treatment at about 900° C. Thisundesirable low electrode density ultimately leads to low volumetriccapacities in practical lithium-ion cells.

[0005] Denser oxides can be obtained using a synthesis constituted by amore controlled co-precipitation followed by treatment at temperaturesgreater than or equal to 1100° C. with a slow cooling to preserve cellperformance. Such a synthesis, however, is not completely suitable forindustrial applications because the controlled precipitation process isdifficult and is expensive due to energy requirements to achieve thehigh heat treating temperatures. Also, oxides synthesized this wayexhibit high first cycle irreversible capacity, thus limiting theiruseful capacity when used in a battery.

[0006] It is known in the art that LiF used in producingLi_(1+x)Mn_(2−x−y)M_(y)O_(4−z)F_(z) (with 0<x<=0.15, 0<y<=0.3, and0<z<=0.3, and M is a metal comprised of at least one of Mg, Al, Co, Ni,Fe, Cr), can function as a flux for lithium ion electrode materials. Theart recognizes that this compound has a spinel crystal structure.Further it is known in the art that a spinel structure requires thenominal ratio of lithium to transition-metal to oxygen in the compoundof 1:2:4. LiF is incorporated into the crystalline structure, i.e., mainphase, of the lithium transition metal oxide.

[0007] The art describes H₃BO₃ as a raw material in the synthesis ofLi[(Ni_(0.5)Mn_(0.5))_(1−x−y)M_(x)B_(y)]O₂ (where 0<=x<=0.10,0<=y<=0.05, and M is one of V, Al, Mg, Co, Ti, Fe, Cu, Zn) which can beused as a positive electrode active material. The amount of Co in thiscompound can be up to 10 atomic percent of the amount of lithium in thesynthesized lithium material. The art teaches away from increasingdensity of this material in the belief that increased density leads toinferior cell performance.

BRIEF SUMMARY OF THE INVENTION

[0008] Briefly, a method of producing Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂wherein 0.025≦x≦0.45 and 0.9≦y≦1.3, includes mixing[Ni_(x)Co_(1−2x)Mn_(x)](OH)₂ with LiOH or Li₂CO₃ and one or both ofalkali metal fluorides (preferably LiF) and boron compounds (forexample, boric acid, boron oxide, and/or lithium borates), hereinafterreferred to as sintering agent, and then heating the mixture for a timesufficient to obtain a densified composition ofLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂, the product being sufficiently densefor use in a lithium-ion battery. Compositions so densified exhibit aminimum reversible volumetric energy characterized by the formula[1833−333x] measured in Wh/L, wherein x is as previously defined, andwherein the densified compound is substantially free of F. Preferably xhas a value in the range of 0.05 to 0.45 and y has a value in the rangeof 1.0 to 1.1.

[0009] Although dense oxides can also be obtained using a synthesisincluding a heating step at high temperature (1100° C.), such a heattreatment is not considered suitable for industrial applications because1100° C. heating places severe constraints on furnaces that do not applyfor about 900° C. heating.

[0010] In a preferred embodiment, the density is increased by using asintering agent involving about 0.1 to about 5.0 wt %, preferably about0.2 to about 3.0 wt %, more preferably about 0.5 to about 1.0 wt %, ofone or both of lithium fluoride and boron oxide at a heating temperatureof approximately 900° C. during the synthesis ofLi[Ni_(x)Co_(1−2x)Mn_(x)]O₂.

[0011] This process provides a product with advantages of increaseddensity, low irreversible capacity, and enhanced cathode performancesuch as greater reversible volumetric energy. Useful pellet densityvalues are in the range of about 3.3 to about 4.0 g/cm³, and preferablyabout 3.4 to about 4.0 g/cm³.

[0012] The sintering temperature can be in the range of 800° C. to lessthan 1100° C., preferably 850° C. to 1050° C., and more preferably about900° C. Higher temperatures increase the processing cost and there isless availability of suitable processing equipment.

[0013] The lithium transition metal oxides of the invention have alayered α-NaFeO₂ structure that requires a nominal ratio of lithium totransition metal to oxygen of 1:1:2.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014]FIG. 1 shows the theoretical density (XRD) ofLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ as a function of x obtained throughx-ray diffraction.

[0015]FIGS. 2a and 2 b graphically illustrate pellet density (PD) forLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ prepared at 900° C. as a function of LiFaddition for x=0.25 (FIG. 2a) and x=0.1 (FIG. 2b) composition.

[0016]FIG. 3 shows the BET surface area and pellet density evolutions asa function of wt % LiF added in Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ forx=0.1.

[0017]FIGS. 4a and 4 b graphically illustrate x-ray diffraction patternsfor Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ for x=0.25 (FIG. 4a) and x=0.1 (FIG.4b) as a function of LiF addition.

[0018]FIGS. 5a, 5 b, and 5 c graphically illustrate the effect of B₂O₃addition on the pellet density of different oxide compositions preparedat 900° C. for 3 hours for x=0.1, 0.25 and 0.375.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019] The present invention includes a method of producing lithiumtransition metal oxides sufficiently dense for use in electrodecompositions, preferably cathode compositions, for lithium-ionbatteries. Compositions having a pellet density of greater than about3.3 g/cm³ can be obtained using a sintering agent selected from thegroup consisting of alkali metal fluorides (for example, LiF and/or KF;preferably LiF), boron compounds (for example, boric acid, boron oxide,and/or lithium borates; preferably, B₂O₃), and mixtures thereof, at alevel of at least about 0.1 wt % of the total weight of the mixture.Higher levels of sintering agent such as about 1.0 wt % also producehigher pellet densities. It is understood that when precursors have ahigh surface area, then greater levels of sintering agents can berequired to produce the same increased pellet density. Levels ofsintering agent as high as about 5 wt % and even up to about 10 wt % canproduce yet even higher pellet densities. At levels of about 3 weightpercent and higher, additional heating time can be required to removeimpurities from the product. Impurities of F, which would be present ina separate phase, are undesirable because their presence reduces thereversible volumetric energy (RVE). The stoichiometry of the lithium inthe starting material can be adjusted to compensate for the additionallithium being added by the use of LiF as a sintering agent.

[0020] The lithium transition metal oxides of the present inventionexhibit certain characteristics that have been discovered as beinguseful for enhancing electrode performance. These characteristicsinclude increased density properties, without increasing theirreversible capacity significantly, and resulting increasedelectrochemical properties including RVE. A density property of interestis pellet density. Pellet density is that density calculated from theweight of lithium transition metal oxide (500 mg were used in themeasurements in the examples of this invention) placed within a moldhaving a known volume (an 8 mm diameter die was used in the measurementsin the examples of this invention), with the lithium transition metaloxide being pressed at approximately 48,000 psi (330,000 kPa). Theresulting calculation gives a weight per volume quantity or density. Thepellet density can be compared against theoretical density to ascertainthe extent of densification of the lithium metal oxide. The theoreticaldensity (ThD) is defined as follows:

ThD(g/ml)=[10²⁴(MW)(N)]/[(CV)(NA)].

[0021] where 10²⁴ is the number of cubic angstroms per milliliter, MW isthe molecular weight of the compound expressed in grams per mole, N isthe number of molecular units per unit cell, CV is the volume of theunit cell expressed in cubic angstroms per unit cell and NA isAvogadro's number (6.023×10²³ molecular units per mole). A unit cell isa small repeating physical unit of a crystal structure. The type ofstructure and lattice constants, which together give the unit cellvolume, can be determined by x-ray diffraction. Because the presentmaterials have the α-NaFeO₂ structure-type, the cell volume can becalculated from the lattice constants a and c as follows:

CV=(a ²)(c)(cos(30°))

[0022] An electrochemical property of interest with regard to thepresent invention is reversible volumetric energy (RVE).

RVE=(DSC ₁)(V _(aveD))(ED)(DSC ₁ /CSC ₁).

[0023] RVE (reversible volumetric energy) (watt-hours per liter) is theamount of electrical energy stored per unit volume of the cathodeelectrode that can be recycled after the first charge. RVE values of theinvention preferably are in the range of about 1500 to about 2200 Wh/L,more preferably in the range of about 1750 to about 2200 Wh/L.

[0024] DSC₁ (First Discharge Specific Capacity) (milliamp-hours pergram) is the amount of electrical charge passed by a battery per gram ofcathode oxide during first discharge.

[0025] V_(aveD) (volts) is the average voltage during discharge from abattery. For the present cathode materials V_(aveD) refers to thevoltage of the cathode versus lithium metal, and values of 3.85 and 3.91V are close approximations of V_(aveD) for x=0.25 and x=0.10respectively and shall be assumed in calculations of RVE.

[0026] CSC₁ (First Charge Specific Capacity (milliamp-hours per gram))is the amount of electrical charge passed by a battery per gram ofcathode oxide during first charge.

[0027] ED (electrode density) (gram per milliliter) is the density ofthe cathode electrode, and shall be considered to be 90% of the pelletdensity.

[0028] Capacities of a battery described herein are those obtained whencycling the battery at 40 milliamp per gram of cathode oxide.

[0029] The lithium transition metal oxide of the present invention wasprepared using a co-precipitation process to form a transition-metalhydroxide (TMOH). The precipitated TMOH was then mixed by grinding witha combined amount of Li(OH).H₂O and sintering agent. Li₂CO₃ can be usedinstead of LiOH. After grinding, pellets were formed and then heated toabout at least 900° C. for about 3 hours, and quenched. After quenching,the pellets were ground and the resulting powder was used to makecathodes. Although pellets were made, it is understood that the groundmixture of TMOH and lithium salts can be subjected to heat treatmentwith essentially the same results for a heated loose powder.

[0030] The present invention is more particularly described in thefollowing examples, which are intended as illustrations only and are notto be construed as limiting the present invention.

EXAMPLES

[0031] The lithium metal oxides of the present invention were preparedusing the following as starting materials: LiOH.H₂O (98%+, AldrichChemical Co., Milwaukee, Wis.), CoSO₄.7H₂O (99%+, Sigma-Aldrich Co. ofHighland, Ill.), NiSO₄.6H₂O (98%, Alfa Aesar, Ward Hill, Mass.), andMnSO₄.H₂O (Fisher Scientific, Hampton, N.H.). Where not designated,chemicals were obtained from Aldrich Chemical Co., Milwaukee, Wis. Allpercentages were by weight.

[0032] The process to densify lithium metal oxides of the presentinvention included two steps. The first step involved a co-precipitationof transition metal sulfate salts in a stirred solution of LiOH toobtain a co-precipitate. It is understood that a solution including anyone or more of LiOH, NaOH, and NH₄OH can be used as the precipitatingagent, leading to the same final improvement in density describedherein. The second step comprised mixing the co-precipitate withstoichiometric amounts of Li(OH).H₂O and one or both of LiF and B₂O₃(both available from Aldrich Chemical Co.), forming a pellet and heatingthe pellet to at least about 900° C.

[0033] In performing the first step, a 100 ml aqueous solution of thetransition metal sulfates (CoSO₄.7H₂O , NiSO₄.6H₂O and MnSO₄.H₂O) (totalmetal concentration equal to 1M) was dripped into a stirred aqueoussolution of 1 M LiOH. A chemical metering pump manufactured by LiquidMetering Inc. of Acton, Mass. was used at a constant speed and strokefor 1 hour of co-precipitation. LiOH concentration was kept constantduring the co-precipitation process by metering a sufficient amount of 1M LiOH to keep the pH controlled at 14. The co-precipitant produced wasNi_(x)Co_(1−2x)Mn_(x)(OH)₂ where x is as previously defined. Theprecipitate was filtered, washed several times with distilled water,dried in air at 120° C. overnight and then ground for 5 minutes tode-agglomerate the powder.

[0034] The dried precipitate was then mixed (by grinding) with astoichiometric amount of Li(OH).H₂O and selected amounts of one or bothof LiF and B₂O₃ (0, 0.2, 0.5, 1, 3, 5 wt % of the theoretical oxidemass) (Aldrich Chemical Co.) to keep the desired lithium stoichiometry(1 mole per total moles of transition metal) in the final oxide. Aftergrinding, pellets were made, heated at 900° C., some for 3 hours andsome for 6 hours and then quenched between copper plates. The pelletswere quenched to save time. The pellets could have been air cooledslowly with essentially the same results. Once the pellets were cooled,they were broken up and ground.

[0035] X-ray diffraction (XRD) was used to determine which crystallinephases were present in the sample and the structural characteristics ofthose phases. The data was collected using an X-ray diffractometerfitted with a fixed entrance slit with 1 degree divergence, a fixed 0.2mm receiving slit (0.06 degrees), a graphite diffracted beammonochromator, and a proportional detector for registry of the scatteredradiation. A sealed copper target X-ray source was used at generatorsettings of 40 kV and 30 mA. Profile refinement of the collected datawas made using a Hill/Howard version of the Rietveld program Rietica.The structural model typically used was the α-NaFeO₂ structure with Liin 3a sites, Ni, Co and Mn randomly placed on 3b sites, and oxygen atomson 6c sites. An anti-site defect was assumed wherein Li and Ni exchangedsites, the slight extent of which was calculated as part of the Rietveldrefinement.

[0036] Pellet density (PD) for each sintered set was obtained by making8 mm diameter pellets with approximately 500 mg of ground powder under apressure of 48,000 psi (30,096 kPa). The thickness and diameter of thepellet after pressing was measured and the density was then calculated.The error was estimated to be ±0.08 g/cm³.

[0037] In order to develop the correlation between pellet density andelectrode density, test electrodes of five differentLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂, wherein x and y are as previouslydefined, were made. Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ (90 parts), SUPER Scarbon black (5 parts) (MMM Carbon, Tertre, Belgium), and polyvinylidenedifluoride (PVDF) (5 parts) binder were combined to make electrodematerial. The electrode material was made into a slurry using n-methylpyrrolidinone (NMP) and the slurry was then coated on aluminum foil. Theelectrode material coated on aluminum foil was dried in a muffle ovenovernight to evaporate the NMP and form a film. The film was pressed at48,000 psi (330,096 kPa). Electrode density was obtained by measuringthe thickness of the film with a digital micrometer and measuring themass of a known area of the film. Five different samples graphicallygave a slope of 0.89 when the intercept was constrained to be zero. Theachievable electrode density was thus considered to be 90% of the pelletdensity.

[0038] In order to perform electrochemical tests, a Bellcore-type cellwas prepared. The Bellcore-type cell included 200 to 300 mm thickPVDF/HFP-based (a copolymer of polyvinylidenefluoride/hexafluoropropylene) positive and negative electrodes and anelectrolyte separator.

[0039] The Bellcore-type cell was prepared by taking z gramsLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ which was mixed with approximately0.1(z) (by weight) SUPER S carbon black and 0.25(z) (by weight) polymerbinder, available under the trade designation KYNAR FLEX 2801 (AtofinaChemicals, Inc. of Philadelphia, Pa.). To this mixture was added 3.1(z)(by weight) acetone and 0.4(z) (by weight) dibutyl phthalate (DBP),available through Aldrich Chemical Co., of Milwaukee, Wis., to dissolvethe PVDF/HFP. Several hours of stirring and shaking were required todissolve the PVDF/HFP and to break apart clumps of carbon black. Theresulting slurry was then spread on a glass plate using a notch barspreader to obtain an even thickness of approximately 0.66 mm. After theacetone had evaporated, the resulting dry film was peeled off the plateand punched into circular disks with a diameter of approximately 12 mm.The punched circular disks (electrodes) were washed several times inanhydrous diethyl ether to remove the DBP. The washed electrodes weredried at 90° C. overnight before use. The electrochemical cells wereprepared in standard 2325 (23 mm diameter, 2.5 mm thickness) coin-cellhardware with a single lithium metal foil used as both the counter andreference electrode. The cells were assembled in an argon-filledglovebox. The electrolyte used for analysis was 1M lithiumhexafluorophosphate (LiPF₆) in ethylenecarbonate-diethlycarbonate(EC/DEC) (33/67). The cells were tested using a constant charge anddischarge current of 40 mA/g (corresponding to approximately 0.6 mA/cm²)between 2.5 and 4.4 V.

[0040]FIGS. 2a and 2 b graphically illustrate the pellet densityevolutions as a function of LiF addition forLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ compositions for x=0.25 (FIG. 2a) andx=0.1 (FIG. 2 b). In both cases, pellet density increased with addedLiF. For x=0.1, the pellet density increased quasi-linearly from about3.3 to about 3.7 g/cm³ until 1 wt % of LiF was added. The valuesstabilized around 3.8-3.85 g/cm³ with further addition of LiF. Opencircles refer to special treatments. A slight excess in lithiumstoichiometry, as noted by open circle “1” in FIG. 2b led to a slightlyhigher pellet density compared to the Li/M=1/1 stoichiometry where M isthe total of transition metals in the compound. Another treatment of 3hours at 900° C. led to another slight increase in pellet density asindicated by samples noted by open circles “2” and “3” in FIG. 2b.

[0041]FIG. 3 shows the correlation between the decrease in BET surfacearea while the pellet density increased as a function of LiF addition inthe case of Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ with x=0.1 (all samplesprepared from the same co-precipitate). The data show the specificsurface area of Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ samples prepared atabout 900° C. decreased and the density increased as the weight percentof LiF increased. Typically, electrode materials with higher specificsurface area can lead to less-safe Li-ion cells by increasing theinterface area between the electrolyte and the electrode grains. Lowerspecific surface area is of interest in increasing the thermal stabilityof the cell.

[0042] Structural data obtained from Rietveld refinements are collectedin Table 1. The α-NaFeO₂ structural type was preserved in all cases andx-ray patterns and lattice constants of the starting compounds werethose typically previously observed for these compositions. TABLE 1Fraction of Ni Sample LiF (wt %) a (Å) c (Å) in Li-layer x = 0.1 02.8310(2) 14.135(2) 0.011(3) x = 0.1 0 2.8312(3) 14.135(2) 0.011(3) x =0.1   0.2 2.8305(2) 14.135(2) 0.000(3) x = 0.1   0.5 2.8297(3) 14.134(2)0.013(3) x = 0.1 1 2.8294(2) 14.131(2) 0.000(3) x = 0.1 1 2.8309(2)14.132(2) 0.009(3) x = 0.1 3 2.8272(3) 14.137(2) not measured x = 0.1 32.8282(3) 14.136(2) 0.005(3) (re-heated 3 hours) x = 0.1 5 2.8228(4)14.132(3) not measured x = 0.1 5 2.8234(3) 14.138(2) 0.006(3) (re-heated3 hours) x = 0.1 5 2.8231(3) 14.142(2) 0.013(3) (re-heated 6 hours) x =0.25 0 2.8493(2) 14.199(2) 0.009(3) x = 0.25   0.5 2.8508(2) 14.208(2)0.016(3) x = 0.25 1 2.8513(2) 14.210(2) 0.011(3)

[0043] The data of Table 1 show that constants a and c were unaffectedby the addition of LiF, indicating that the crystal structure dimensionwas essentially free of LiF.

[0044]FIGS. 4a and 4 b graphically illustrate similar patterns (wt % ofLiF indicated on each pattern) for all samples for both compositionsLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ where x=0.25 (FIG. 4a) and where x=0.1(FIG. 4b) regardless of whether LiF was added except with 3 and 5 wt %LiF addition for x=0.1 wherein some impurity lines clearly appeared(FIG. 4b). For x=0.25 (FIG. 4a), the lattice constants evolution trendwas a minimal increase as LiF increased from 0 to 1 wt % (* in FIG. 4bindicates impurity lines).

[0045] Table 1 also lists the amount of metal defect (Ni) in the Lilayer, calculated as part of the Rietveld refinement, which is known toinfluence the cell behavior. In all cases, as expected for thesecompositions, this amount was very small and no significant change wasnoticed as a function of LiF addition. Table 2 shows cycling data at 40mA/g between 2.5 and 4.4 V for Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O_(2.) withx=0.25 (0, 0.5 and 1 wt % LiF addition), x=0.1 (0 and 1 wt % LiFaddition) and x=0.1 (0, 0.2, 0.5, 1, 3, 3(+3 hours) and 5 wt % LiFaddition).

[0046] Table 2 lists wt % LiF, pellet density for each sample, firstcharge/discharge energy, irreversible capacity and RVE for samples oflithium transition metal oxide where x=0.1 and 0.25. TABLE 2 1^(st)Charge/1^(st) % LiF PD Discharge Irreversible RVE Sample (wt %) (g/cm³)(mAh/g) Capacity (Wh/L) x = 0.1 0 3.4 175/162 7.4 1794 x = 0.1 0 3.3166/150 9.6 1574 x = 0.1   0.2 3.4 157/145 7.6 1602 x = 0.1   0.5 3.5161/153 5.0 1791 x = 0.1 1 3.7 173/163 5.8 2000 x = 0.1 1 3.7 157/1485.7 1817 x = 0.1 3 3.85 141/128 9.2 1574 impurity x = 0.1 3 (re-heated3.94 164/149 9.1 1877 3 hours) x = 0.1 5 3.8 113/96  15   1091 impurityx = 0.25 0 3.2 177/165 6.8 1705 x = 0.25   0.5 3.5 173/161 6.9 1817 x =0.25 1 3.6 173/155 10.4  1732

[0047] The data of Table 2 show that use of LiF gave improved RVE valuescompared to those when no LiF is present. Impurities in the compositionresulted in a marked decrease in RVE values. Capacity retention uponcycling maintained stable and good values with use of LiF. The cycledcapacity was the same, the RVE was improved.

[0048] Comparing Table 2 with FIG. 1, it is preferable that the lithiumtransition-metal oxides of the present invention have a pellet densityof at least about 72%, and more preferable that they have a pelletdensity of at least about 74%, of the theoretical density. Furthermore,it has been found that the reversible volumetric energy of the lithiumtransition-metal oxide of the present invention can be defined by theformula [1833−333x] as measured in Wh/L.

[0049] LiF addition had an effect on increasing the density ofLi_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ oxides to 3.6 g/cm³ for x=0.25 and to3.7 g/cm³ for x=0.1 up to 1 wt % LiF added. This increase in density wasaccompanied by a decrease in BET surface area. Almost no influence onthe materials structure was observed. No difference at all in materialstructure was found for x=0.1 composition up to and including additionsof LiF as high as 1 wt % for lattice constants (a) and (c) (Table 1) andcell behavior (Table 2). At and above about 3 wt % addition of LiF, a“LiF impurity” containing some transition metal appeared and led tolower cell performances for the oxide. It was found that another 3 hourstreatment at about 900° C. of the 3 wt % LiF addition led to a materialwithout impurity, same lattice constants (a) and (c) as without anyadditive, and with the same cell behavior as the lower amount LiFaddition samples but having a higher density of about 3.9 g/cm³. It wasalso found that LiF additions above about 10% by weight were believed toadd fluorine to the structure of the transition metal oxide. Using otheralkali metal fluorides, such as KF as sintering agents, desirable pelletdensity values and RVE values can be obtained when using the proceduresdescribed above.

[0050]FIGS. 5a, 5 b and 5 c graphically illustrate the effect of boronoxide addition on the pellet density of different oxide compositionsprepared at 900° C. for 3 hours. All samples for each composition wereobtained from the same co-precipitate. The graphs show pellet densityfor oxides prepared at 900° C. for 3 hours for 3 compositions: x=0.1(FIG. 5a), x=0.25 (FIG. 5b) and x=0.375 (FIG. 5c) as a function of B₂O₃addition. For all compositions, the pellet density increased as afunction of boron oxide content.

[0051] Table 3 lists wt % B₂O₃, pellet density for each sample, firstcharge/discharge energy, irreversible capacity and RVE for samples oflithium transition metal oxide where x=0.1 and 0.25. TABLE 3 FirstCharge/First Wt % PD Discharge % Irreversible RVE Sample B₂O₃ (g/cm³)mAh/g Capacity (Wh/L) x = 0.1 0 3.3 174/154 11.5 1583 x = 0.1 0.5 3.4163/147 9.8 1586 x = 0.1 1 3.5 166/151 9.0 1692 x = 0.25 0 3.35 163/1526.7 1645 x = 0.25 0.5 3.4 172/153 11.0 1603 x = 0.25 1 3.5 173/147 15.01515

[0052] Table 3 shows that for x=0.1 the resulting increase in RVE ongoing from 0 to 1 wt % B₂O₃ is from 1583 to 1692 Wh/L. Using other boroncompounds, such as boric acid and lithium borates as sintering agents,desirable pellet density values and RVE values can be obtained whenusing the procedures described above.

[0053] Although the present invention has been described with referenceto preferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A method of producing Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ wherein0.025≦x≦0.45, and 0.9≦y≦1.3, the method comprising: mixing[Ni_(x)Co_(1−2x)Mn_(x)]OH₂ with LiOH or Li₂CO₃ and one or both of alkalimetal fluorides and boron compounds as sintering agent; and heating theresulting mixture until a sufficiently dense composition ofLi_(y)[Ni_(x)Co¹⁻²Mn_(x)]O₂ is obtained for use in a lithium-ionbattery.
 2. The method of claim 1 wherein the resulting mixture isheated to at least about 900° C.
 3. The method of claim 1 wherein theresulting mixture is heated for at least about 3 hours.
 4. The method ofclaim 1 wherein the resulting mixture is heated for at least about 6hours.
 5. The method of claim 1 wherein the amount of sintering agentbeing mixed is about 0.1 to about 5.0 weight percent of the resultingmixture.
 6. The method of claim 1 wherein the amount of sintering agentbeing mixed is in the range of about 0.2 to about 3.0 weight percent ofthe resulting mixture.
 7. The method of claim 5 wherein the resultingmixture is heated for about 3 hours.
 8. The method of claim 1 whereinthe amount of sintering agent being mixed is less than about 10 weightpercent of the resulting mixture.
 9. The method of claim 1 characterizedby the resulting densified composition exhibiting a reversiblevolumetric energy of at least about [1833-333x] measured in Wh/L,wherein 0.025≦x≦0.45.
 10. The method of claim 1 wherein the pelletdensity of the resulting densified composition is at least about 72percent of theoretical density.
 11. The method of claim 1 wherein theresulting densified composition has a pellet density in the range ofabout 3.3 to about 4.0 g/cm³.
 12. The method of claim 1 wherein saidsintering agent is an alkali metal fluoride.
 13. The method of claim 12wherein said sintering agent is LiF.
 14. The method of claim 1 whereinsaid sintering agent is a compound of boron.
 15. The method of claim 14wherein said sintering agent is selected from the group consisting ofboron oxide, boric acid, and lithium borates.
 16. A lithium transitionmetal oxide composition produced by the method of claim 1 and exhibitinga minimum reversible volumetric energy characterized by the formula[1833−333x] measured in Wh/L, wherein 0.025≦x≦0.45.
 17. A lithiumtransition metal oxide for use in a lithium-ion battery having thegeneral formula of Li_(y)[Ni_(x)Co_(1−2x)Mn_(x)]O₂ wherein 0.025≦=x≦0.45and 0.9≦y≦1.3 and exhibiting a minimum reversible volumetric energycharacterized by the formula [1833−333x] measured in Wh/L.
 18. Thelithium transition metal oxide of claim 16 exhibiting a pellet densityof at least about 72% of theoretical density.
 19. The lithium transitionmetal oxide of claim 17 exhibiting a pellet density of at least about72% of theoretical density.
 20. The lithium transition metal oxide ofclaim 19 that is formed into a lithium ion battery electrode having areversible volumetric energy in the range of about 1500 to about 2200Wh/L.